Electric lamp apparatus having diffusion barrier

ABSTRACT

Improved electric lamp apparatus exhibiting reduced bulb wall darkening includes a diffusion barrier adjacent the interior of the lamp envelope wall in the vicinity of the lamp electrode or electrodes. Diffusion barrier may be a wire-like mesh or grid spaced from the inner surface of the envelope and adjacent thereto, or a plurality of discrete particulate members in contact with and resting upon the inner surface of the lamp, projecting inwardly into the volume of the lamp envelope. Diffused specie emanating from the electrode selectively deposits upon the diffusion barrier leaving the adjacent envelope wall clear.

United States Patent Witting 1 1 Aug. 8, 1972 ELECTRIC LAMP APPARATUS HAVING DIFFUSION BARRIER Primary ExaminerRoy Lake Assistant Examiner-Darwin R. Hostetter Attorney-John F. Ahern, Paul A. Frank, Richard R. Brainard, Jerome C. Squillaro, Frank L. Neuhauser, Oscar B. Waddell and Joseph B. Forman lmproved electric lamp apparatus exhibiting reduced bulb wall darkening includes a diffusion barrier adjacent the interior of the lamp envelope wall in the vicinity of the lamp electrode or electrodes. Diffusion barrier may be a wire-like mesh or grid spaced from the inner surface of the envelope and adjacent thereto, or a plurality of discrete particulate members in contact with and resting upon the inner surface of the lamp, projecting inwardly into the volume of the lamp envelope. Diffused specie emanating from the electrode selectively deposits upon the diffusion barrier leaving the adjacent envelope wall clear.

ABSTRACT 3 Claims, 4 Drawing Figures TRANSMISSION PAST THE GRID /0) ENVELOPE WALL 2O GRID HEIGHT H PATENTEDAut 8 m2 SHEET 1 [1F 2 FIG.

FIG. 2

nv H H F0 1 T m was 4 2 4 5 GRID HEIGHT H V VENTO/P. HARALD L W/TTl/VG', by H/S ATTORNEY PATENTED M19 8 I973 SHEET 2 0F 2 ENVELOPE WALL www w @864 5 IO I5 20 GRID HEIGHT H llVVE/V TOR HARALD L. W/TT N6, y H/S ATTORNEY The present invention relates to electric lamp apparatus having improved diffusion barriers for the prevention of bulb wall darkening. More particularly, the invention relates to such devices in which the diffusion barrier is associated with the inner surface of the lamp envelope wall, rather than with the electrode which is the source of the wall darkening specie.

In the operation of electric discharge devices, such as electric lamps, the filaments or cathode electrodes thereof are usually raised to elevated temperatures, either to cause direct incandescent radiation therefrom, to sustain a light emitting or stimulating electric discharge, or to emit electrons thermionically. In all cases, the specie of which the electrode so heated is fabricated is caused to dissipate by one or more of several mechanisms, including evaporation, sputtering, and sublimation. Material so removed from the heated electrode or electrodes is generally deposited upon the inner surface of the envelope wall.

Deposition of electrode material upon the envelope wall has several detrimental effects. In lamps, darkening of the bulb wall reduces the transparency of the envelope and decreases light output therethrough. The deposited specie absorbs radiation and becomes heated, raising the temperature of the lamp and accelerating the deterioration of the electrodes. Additionally, films formed by deposition of metallic specie upon the interior of the bulb wall are usually conducting and cause leakage currents along the surface of the envelope wall, thus decreasing lamp efficiency and further increasing lamp operating temperature.

In the prior art, much work has been done to minimize the diffusion of such specie from the electrodes to the bulb wall. Other than gaseous transport cycles such as the iodide transport cycle, most such work has been concentrated on the problem of retaining electrode material at the electrodes, and has resulted in various means such as floating shields and the like, surrounding or closely adjacent the electrodes. To some extent, the foregoing efforts have increased electrode life, have retarded diffusion to the walls and slowed down the wall darkening process. These efforts, have not, however, been completely effective to prevent wall darkening of the lamp envelope walls. Attempts to completely inhibit wall darkening by interposing mechanical shields in the vicinity of the cathode, have a point of diminishing return beyond which the detriment incurred outweighs the benefit. Thus, for example undue emphasis on such structures tends to cause ion trapping and, in discharge lamps, interferes with the lamp discharge, increases the potential drop at the cathode electrode and in general reduces electrode life. Such shields also block some light output directly.

Accordingly, it is an object of the present invention to reduce bulb wall darkening of electric lamp apparatus without disadvantageously affecting the electrode efficiency or life.

Still another object of the present invention is to provide electric lamp apparatus having reduced bulb wall darkening.

Yet another object of the present invention is to provide electric lamp apparatus in which wall darkening is minimized without affecting electrical performance or reducing light output.

Briefly stated, in accord with the one embodiment of the present invention, I provide electric lamp apparatus including a heated electrode in an hermetically sealed light transmissive envelope. A partial pressure of at least a few torr of a buffer gas, such as argon, is provided therein. A diffusion barrier, which may be wirelike grid or mesh spaced from, or a plurality of discrete members attached to the inner surface of the bulb wall envelope, is located at the bulb wall. Vapors and particles of specie removed from the heated electrode preferentially deposit on the diffusion barrier, leaving the envelope wall relatively clear.

The novel features believed characteristic of the present invention are set forth in the appended claims. The invention itself, together with further objects and advantages thereof, may best be understood by reference to the foregoing detailed description taken in connection with the appended drawing in which:

FIG. 1 is a schematic vertical cross-sectional view of a fluorescent lamp envelope embodying the invention,

FIG. 2 is a graphical plot illustrating the diffusion masking abilities of the grid type embodiment of a diffusion barrier in accord with the invention,

FIG. 3 is a graphical plot similar to that of FIG. 2, illustrating the masking abilities of the discrete particulate embodiment of the diffusion barrier, and

FIG. 4 is a vertical cross-section view of an incandescent lamp in accord with the present invention.

In FIG. 1, a vertical cross-sectional view of a fluorescent lamp with the center portion broken away, in order to illustrate two different end structures including different diffusion barriers in accord with the present invention, is illustrated at 10. Lamp 10 includes alight transmissive, hermetically sealed envelope 11 having a pinch 12 at one end thereof with a pair of lamp terminal inleads 13 extending thereinto. Each of the inleads 13 is connected with a flat ribbon 14 which ribbons are enclosed within pinch l2 and are connected by spot welding, for example, to the respective ends of a fluorescent lamp type filament 15, the structure of which is conventional and well-known to those skilled in the art. Within the portion of the lamp envelope immediately surrounded by envelope 11, a diffusion barrier 16 comprising individual wire members 17 is juxtaposed so as to surround laterally the filament electrode 15 and to shield the same from direct line-of-sight communication with the interior of the bulb envelope wall. Diffusion barrier 16 is spaced a distance which is equivalent to several times the diameter of the individual wire members 17 or, in the aggregate, several times the average diameter thereof. Preferably, it has been found experimentally that the diffusion barrier 16 should be spaced apart from the bulb wall interior by a distance of approximately 2 to 1.0 times the average diameter of the individual member 17. It has also been determined experimentally that the spacing between individual members 17 of diffusion barrier 16 should be several times the average diameter of members 17 and, for optimum performance of the diffusion barrier, the inter-member spacing should be within the range of ap proximately 4 to 10 times the average diameter of members 17.

Diffusion barrier 16 may be a plurality of single lateral members or a single spiral-like wire member or, in the alternative, may be a properly dimensioned, in accord with the foregoing criteria, wire mesh which is similarly juxtaposed a predetermined distance from, but adjacent to, the interior of the bulb envelope wall. In the portion of lamp illustrated in the right hand portion of FIG. 1, a crossed grid or mesh diffusion barrier lamp structure includes filament 21 which is laterally surrounded by diffusion barrier 22 which comprises transverse members 23 and longitudinal members 24 comprising a mesh as described hereinbefore.

The material of which the grid is fabricated is not particularly critical. Since no electric potential is required to be placed thereupon, the grid or mesh members may be conducting or nonconducting, although in general, fabrication technology generally favors the use of malleable metallic members. It is naturally required that the material from which the diffuion barrier is constructed should be inert in the presence of any substance constituting the discharge medium. Thus, for example, if a mercury arc is a source of light or of excitation in the lamp environment, the material from which the diffusion barrier is fabricated should not react at the temperature and other characteristic parameters of the discharge with the mercury vapor. Similarly, if a sodium vapor discharge is utilized for light emission or stimulation within the envelope, the diffusion barrier should not be reactive therewith.

An atmosphere of a few torr, or higher, of a buffer gas such as argon or other noble gas is also included. If a mercury discharge lamp or a mercury-metallic vapor lamp or sodium vapor lamp embodies the invention, the envelope also includes a charge of the discharge sustaining and/or light emitting medium. If mercury is present for this purpose, it also serves as the buffer gas, if desired.

FIG. 2 comprises curves illustrating the improvement attained in tests of grid type embodiment of the invention, which tests record the transmission past the members of the diffusion barrier as a function of the distance, herein denominated as the height, of the barrier from the bulb wall and of the inter-member spacing within the diffusion barrier structure, herein denominated as grid spacing. Curves for grid spacing equivalent to 4, 6, 8, and 10 times the average diameter of the members comprising the structure of the diffusion barrier are plotted as a function of the grid height. As may be seen from the curves, which are exponential, a rapid drop occurs from an extrapolated zero height to a height of approximately two times member dimension, at which transmission past the grid has fallen to the value of less than 50 percent for the widest spacing and less than percent for a spacing of four times the average member dimension. From the curve of FIG. 2, it may also readily be seen that, with the barrier a distance of approximately 10 inter-member spacings from the envelope wall, the values of the transmission have fallen to less than 20 percent for all spacing values and less than 4 percent for spacing of 4 times the dimension. Further height increases tend to make the structure rather fragile, due to the support structure required.

From a consideration of the curves of FIG. 2, it is readily apparent that the present invention results in a very substantial diminution of the amount of specie evolved from a heated electrode in an electric lamp apparatus which is permitted to deposit upon the lamp envelope wall. It has been found, as illustrated in the curve of FIG. 2, that the degree of diminution of deposited specie upon the bulb wall is greatly disproportional to the actual physical masking caused by the diffusion barrier, in that only a fraction of the area to be masked need be obstructed with the members of the diffusion barriers in order to diminish by an extent of in excess of 50 percent and readily in excess of percent of the amount which would ordinarly pass in the absence of the barrier. Thus, in accord with the present invention, it is possible to interpose a barrier adjacent the electrode in electric lamp devices which in of itself does not appreciably detract from the light transmissive character of the lamp envelope, while simultaneously greatly diminishing the amount of metallic specie from the lamp electrodes which is permitted to deposit upon the lamp envelope wall to cause the darkening thereof.

In accord with another embodiment of the present invention, the dilTusion barrier may comprise a plurality of discrete members, physically in contact with the surface of the envelope wall and extending a distance into the envelope volume. Such discrete diffusion barriers may constitute, in phosphor coated lamps, exceedingly large phosphor particles. Alternatively, the discrete members may constitute glass grit which is sintered into place or otherwise affixed to the interior of the lamp envelope wall. In still another alternative, magnetic particles may be oriented so as to be extended into the volume of the lamp envelope a greater degree than their thickness and/or width dimension. In all embodiments in which particles resting upon the surface of the envelope are utilized, the particles extend inwardly into the lamp envelope wall and the degree of effectiveness as a diffusion barrier is dependent upon the ratio of the penetration into the lamp envelope volume to the average thickness dimension of the body in a direction parallel to the lamp envelope wall.

FIG. 3 of the drawing illustrates in graphical form the diminution of transmission of particles evolved from the electrodes of lamps in accord with the present invention by the interposition of a discrete member type of diffusion barrier. In FIG. 3, the degree of diminution for member spacings, which vary from 5 to 13 times the average particle thickness dimension, are plotted as a function of the ratio of the distance the members extend inwardly into the volume to the average thickness dimension of the members. As may be seen from the drawing, the curves indicating inter-member dimension-to-member dimension ratios of 5, 7, l0, and 13, fall off rapidly from a transmission value of percent to a value of less than 50 percent at a ratio of approximately 10 and fall below 10 percent for values of the ratio of less than approximately 25. Another parameter of merit is the distance the discrete members extend into the envelope. Preferably such distances should fall within the range of from 5 to 35 times the average dimension of the member parallel to the envelope wall.

The advantages of the diffusion barriers in accord with the present invention may be achieved with a variety of lamp structures. Thus, for example, FIG. 1 illustrates a fluorescent lamp embodying the invention.

In FIG. 4 of the drawing, an incandescent lamp, identified generally as 30, embodying the invention, includes a light transmissive envelope 31 and a screw base 32 having respective contact members 33 and 34. A glass pinch 35 supports filament support members 36, between which a filament 37 is suspended. A diffusion barrier 38 composed of a plurality of wire-like grid members 39 is juxtaposed adjacent and spaced from, the interior of the wall of envelope 31, in the general vicinity of the filament. The invention may similarly be utilized in the construction of high pressure mercury vapor lamps or of other type metallic vapor lamps such as disclosed and claimed in Reiling U.S. Pat. No. 3,231,421 and in Schmidt US. Pat. No. 3,245,590.

In all such lamps, the same general criteria are followed and it is found that the closeness of the spacing of the individual members of a diffusion barrier and the degree of penetration of the barrier into the volume of changes as fall within the true spirit and scope of the present invention.

What I claim as new and desire to secure by Letters Patent from the United States is:

1. Electric lamp apparatus comprising:

a. an evacuable hermetically sealed light transmissive envelope;

b. an electrode member extending into said envelope and adapted to be heated to an operating temperature at which a constituent thereof is evolved and enters the volume of said envelope;

c. a partial pressure of at least a few torr of a buffer gas within said envelope;

d. a diffusion barrier juxtaposed immediately adjacent the inner surface of said envelope in the vicinity of said electrode member and adapted to collect said evolved constituent and prevent deposition thereof upon said envelope wall; and

e. wherein said diffusion barrier comprises a plurality of desc'rete members contacting said envelope wall and extending into said envelope volume.

2. The apparatus of claim 1 wherein said discrete members are spaced apart from one another by an average distance that is approximately 5 to 13.5 times the average dimension thereof parallel to said envelope wall.

3. The apparatus of claim 1 wherein said discrete members extend into the volume of said envelope an average distance that is approximately 5 to 35 times the average dimension of said members parallel to said envelope wall. 

1. Electric lamp apparatus comprising: a. an evacuable hermetically sealed light transmissive envelope; b. an electrode member extending into said envelope and adapted to be heated to an operating temperature at which a constituent thereof is evolved and enters the volume of said envelope; c. a partial pressure of at least a few torr of a buffer gas within said envelope; d. a diffusion barrier juxtaposed immediately adjacent the inner surface of said envelope in the vicinity of said electrode member and adapted to collect said evolved constituent and prevent deposition thereof upon said envelope wall; and e. wherein said diffusion barrier comprises a plurality of descrete members contacting said envelope wall and extending into said envelope volume.
 2. The apparatus of claim 1 wherein said discrete members are spaced apart from one another by an average distance that is approximately 5 to 13.5 times the average dimension thereof parallel to said envelope wall.
 3. The apparatus of claim 1 wherein said discrete members extend into the volume of said envelope an average distance that is approximately 5 to 35 times the average dimension of said members parallel to said envelope wall. 